In the treatment of webs of fabric or the like, where a liquid is applied to or removed from the web (see the aforementioned copending applications and the concurrently filed copending application Ser. No. 949,697, it is important that the treatment be uniform over the entire width of the web.
This can only be achieved when the pressure with which the working roll and the counterroller are pressed together is substantially constant and uniform over the entire machine width, corresponding to the width of the web.
A problem which always appears to arise in this connection is the bending of the rollers as a consequence of the relatively high working width (and roller length). This bending is greater as the diameter of a roller or drum is smaller, the wall thickness of the roller or drum is less and the length of the roller or drum is greater.
In order to simplify maintenance, repair and other handling of the rollers, it is advantageous to make them relatively light and of smaller diameter. This, of course, increases the problem of bending.
There are a number of approaches to solve this problem. For example, it is known to provide rollers which are pressurized internally by hydromechanical means and thus are intentionally deformed to overcome the bend effect These systems are complex to fabricate and expensive to maintain and require the delivery of a hydromechanical medium to the interior of the roller, so that for this purpose alone it must have a relatively larger diameter the. The axial journaling of such rollers is also expensive and complicated and roller replacement is costly.
In practice, the problem of bending is attacked by making the rollers of rubber and grinding them so that they have a bulging shape. However, such rollers shaped to overcome the effect of bending can only be used effectively at a single press pressure and thus provide uniform results only for a single web width. It is, therefore, necessary to frequently change the rollers for the desired pressure and web width. This means frequent standstill of the machine which is not economical.